Fix deprecated image reference in readme
Fix deprecated image reference in readme

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Signed-off-by: Roman Mazur <238a1843d81dd7fbe80b5c1b99515c4ba8c94d0d@balena.io>

linux-on-ibm-z/cadvisor,linux-on-ibm-z/cadvisor,linux-on-ibm-z/cadvisor